He said more than £9bn is spent annually by the public sector in Scotland procuring goods and services from the private sector, however, in 2011, 28% of private sector employees were paid less than £7.20 an hour.

Mr Park said: "Six out of 10 Scots children live in families suffering from in-work poverty.

"We have seen a commitment from a range of public sector bodies to pay their employees the lliving wage but I believe we must go further.

"I believe that if we do not take action on this issue then we are letting down thousands of low-paid, hard-working Scots."

But there is a question over whether it is legal to force a living wage as a condition of any public contracts.

Ministers have been advised it would breach European Union law. However, Mr Park said he has legal advice which says it would not.

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